Communication system, transmission device, reception device, and communication method

ABSTRACT

There is provided a communication system capable of achieving a high usage efficiency of frequencies without the need for cooperation of multiplexed users. A communication system communicates over frequency channels set by dividing a frequency bandwidth assigned to the system allows interference between channels by overlapping the adjacent frequency channels with each other in the frequency domain, or a transmitting and receiving device, which transmits and receives a signal by allowing the interference between symbols at a waveform level for each channel to decrease the occupied bandwidth, is provided with ICI removal and ISI compensation filter  111  serving as either an ICI removal filter for removing the interference between channels or an ISI compensation filter for compensating the interference between symbols.

TECHNICAL FIELD

The present invention relates to communication systems, transmittingdevices, receiving devices, and communication methods, and morespecifically, to a communication system, transmitting device, receivingdevice, and communication method, applied to an environment in which asingle or multiple frequency channels are used for communication,without the need for cooperation among multiplexed users.

BACKGROUND ART

Signals from multiple users are multiplexed and transmitted to a basetransceiver station. The multiplexing technique is also referred to asmultiple access. As a method for multiple access, FDMA (FrequencyDivision Multiple Access) and OFDMA (Orthogonal Frequency DivisionMultiple Access) are well known. FDMA is a method of dividing thefrequency range with a limited spectrum over a frequency axis, assigningthe divided frequencies to respective users, and multiplexing thefrequencies for transmission. OFDMA is translated as orthogonalfrequency division multiplexing, and is a method of orthogonalizing thespectrums of adjacent channels with each other.

As known documents describing OFDMA, for example, there are Non-PatentDocument 1 and Non-Patent Document 2. As known documents describingFDMA, for example, there are Non-Patent Document 3 and Non-PatentDocument 4.

In each of OFDMA and FDMA, since multiple data streams are transmittedin parallel, each stream is transmitted over a single frequency channel.For this reason, in order to prevent the interference between therespective frequency channels (frequency bands), the configuration willbe made as described below.

FIG. 20 shows frequency spectrums of OFDMA. FIG. 20 shows a case wherethere are six frequency channels in the system overall bandwidth W₁, asan example of OFDMA frequency spectrums. According to OFDMA, multipleusers (user 1 to user M) each transmit data by use of some of themultiple spectrums shown in FIG. 20. (FIG. 20 shows an example casewhere the user 1 uses two frequency channels, the user k uses a singlefrequency channel, and the user M uses three frequency channels.) InOFDMA, by overlapping adjacent frequency channels, the entire systembandwidth can be made small and the usage efficiency of the spectrum canbe improved. However, to maintain orthogonality of adjacent frequencychannels, constraints on the time synchronization of the multiplexedusers are to be met. Non-Patent Document 1 and Non-Patent Document 2describe that when the users cannot keep cooperation in transmission,the orthogonality of signals is destroyed and the characteristics ofdata transmission is significantly degraded.

FIG. 21 shows frequency spectrums of FDMA. FIG. 21 shows a case wherethere are six frequency channels in the system bandwidth W₂, as anexample of FDMA frequency spectrums. As described in Non-Patent Document3, in FDMA, guard bands are provided between adjacent frequency channelsto prevent the interference between the frequency channels to be used bythe respective users. As a result, the entire system bandwidth of theFDMA system is greater than that of the OFDMA system, whereas the FDMAsystem has an advantage of eliminating the constraints on temporalsynchronization among users. Nevertheless, the signal waveform thatavoids the Inter-Symbol Interference in each frequency channel has to beemployed for the FDMA system to maintain the signal quality in eachchannel. In order to avoid Inter-Symbol Interference at such a waveformlevel, the pulse waveforms of the signals are shaped based upon Nyquistcriterion.

In FDMA, it is desirable to make smaller the intervals between thefrequency channels, so that the frequency use efficiency is improved bymaking smaller the entire system bandwidth. For instance, FIG. 22 showsa case where the intervals between the frequency channels are madenarrower by making the guard bands smaller. FIG. 23 shows a case wherethe intervals between the frequency channels are made narrower by makingsteep the pulse waveform of each frequency channel. Additionally,Non-Patent Document 4 describes a method of making narrower thebandwidth occupied by each frequency channel by employing PartialResponse method that intentionally introduces Inter-Symbol Interferenceat the information symbol level.

Incidentally, the signal is shaped by a pulse shaping filter. However,when the signals are shaped by a filter with a sharp frequency responseat the frequency domain as shown in FIG. 23, the time responses will begreatly dispersed at the time domain, making it difficult to design sucha filter in practice. Accordingly, for shaping the pulses, a trade-offrelationship exists between the shape in the frequency domain and themagnitude of the temporal dispersion of the shaped pulses in the timedomain.

Non-Patent Document 1: S. B. Weinstem and P. M. Ebet, “Data transmissionby frequency-division multiplexing using the discrete Fouriertransform,” IEEE Trans. Commun., vol. 19, no. 5, pp. 628-34, October1971

Non-Patent Document 2: Burton R. Saltzberg, “Performance of an efficientparallel data transmission system,” IEEE Trans. Commun., vol. 15, no. 6,pp. 805-811, December 1967.

Non-Patent Document 3: J. G Proakis, “Digital Communications,” pp.897-899.

Non-Patent Document 4: J. G Proakis, “Digital Communications,” pp.561-568.

Problems to be Solved by the Invention

It should be noted that, however, it is difficult to sufficientlyimprove the spectrum usage efficiency in the conventional FDMA with theguard bands. That is, in shaping the waveforms, the steep frequencyresponse may decrease the entire system bandwidth, but the possibilityof achieving the pulse shaping filter is difficult in consideration ofthe causality of its temporal response. Therefore, the frequencyresponse has to be made smooth, thereby resulting in the difficulty inmaking the entire system bandwidth sufficiently small.

On the other hand, it is possible to make the entire system bandwidthsmall when OFDMA is employed. However, constraints on the timesynchronization have to be met among users, thereby necessitating thecooperation between multiple users.

Furthermore, in a case where the bandwidth in each frequency channel ismade narrower by use of the Partial Response method, the receivingdevice is subject to a drawback in that error propagation occurs whenthe symbol is decoded and the reception characteristics are degraded,due to the induced ISI (Inter-Symbol Interference) observed at thesymbol level of the received signal.

It is an object of the present invention to provide a communicationsystem, transmitting device, receiving device, and communication method,whereby multiple users do not have to cooperate with each other and highfrequency usage efficiency is achievable.

Means for Solving the Problems

In order to solve the above problems, a communication system accordingto claim 1 is a communication system that communicates over frequencychannels set by dividing a frequency bandwidth assigned to the system,the communication system comprising: a transmitting device thattransmits a signal in which Inter-Channel Interference is allowed bypurposely overlapping among the frequency channels adjacent to eachother in a frequency domain; and a receiving device that receives thesignal transmitted from the transmitting device, the receiving devicecomprising ICI removal means that removes the Inter-ChannelInterference, owing to overlapping adjacent frequency channels with eachother, allowed at the signal transmitted. According to an aspect of thepresent invention, the transmitting device transmits the signal byoverlapping multiple frequency channels with each other, thereby makingthe frequency bandwidth assigned to the system available to otherchannels and improving the usage of the spectrum efficient. Also, thereceiving device is capable of removing the interference generated onthe overlapping frequency regions between frequency channels, therebypreventing the degradation in the signal quality of received signal.

A communication system according to claim 2 is a communication systemthat communicates over frequency channels set by dividing a frequencybandwidth assigned to the system, the communication system comprising: atransmitting device that transmits a signal in which Inter-SymbolInterference at a waveform level for each of the frequency channels isallowed; and a receiving device that receives the signal transmittedfrom the transmitting device, the receiving device comprising ISIcompensation means that compensates Inter-Symbol Interference at thewaveform level between the symbols for each of the frequency channels ofthe signal transmitted. According to an aspect of the present invention,the transmitting device is capable of transmitting the signal with apulse that does not satisfy the zero ISI condition, thereby decreasingthe bandwidth of each frequency channel. Consequently, the frequencybandwidth assigned to the system can be used by more frequency channels,thereby improving the efficiency usage of the spectrum. In addition, inshaping the pulse, the zero ISI condition does not have to beconsidered, thereby improving the design flexibility of the filter forpulse shaping.

Further, since the receiving side is capable of compensating ISI, thedegradation in the signal quality of the received signal can beprevented.

A communication system according to claim 3 is a communication systemthat communicates over frequency channels set by dividing a frequencybandwidth assigned to the system, the communication system comprising: atransmitting device that transmits a signal; a receiving device thatreceives the signal transmitted from the transmitting device; a spectrumusage information and policy information acquiring portion that has afunction to detect a bandwidth of a frequency channel that is not beingcurrently used and to determine usage status of that frequency channel;a pulse shape and symbol rate controller that determines whether or nota user allows ISI and whether or not an adjacent frequency channel foranother user is interfered, based upon the information acquired by thespectrum usage information and policy information acquiring portion, andthat determines at least one of a center carrier frequency, a symbolrate, and a pulse shape, based upon a determination result; and a centercarrier frequency controller that controls a center carrier frequency ofthe signal transmitted with the use of a center carrier frequencydetermined by the pulse shape and symbol rate controller. According toan aspect of the present invention, the transmitting device is capableof detecting the bandwidth of the frequency channel that is not beingcurrently used, determining whether or not it is possible to allow thefrequency channel, for another user, adjacent to the frequency channelto interfere with the frequency channel, and determining at least one ofthe center carrier frequency, symbol rate, the shaped pulse of thesignal to be transmitted, based on the above determination. Accordingly,it is possible to transmit the signal with a pulse shape of a high usageefficiency of the spectrum according to the usage status of thespectrum, while the signal quality of the received signal is beingconsidered.

A transmitting device according to claim 4 is a transmitting device thatcommunicates over frequency channels set by dividing a frequencybandwidth assigned to a system, the transmitting device comprisingsignal transmission means that transmits a signal in which adjacentfrequency channels are overlapped with each other in a frequency domain.According to an aspect of the present invention, the usage efficiency ofthe spectrum to be used for communication can be improved.

The transmitting device according to claim 5 is the transmitting devicein claim 4, wherein the signal transmission means sets overlappingbetween the frequency channels of the signal within an excessivebandwidth of a frequency channel. According to an aspect of the presentinvention, the interference between frequency channels can be suppressedwithin a range where the receiving side is capable of removing.

A transmitting device according to claim 6 is a transmitting device thatcommunicates over frequency channels set by dividing a frequencybandwidth assigned to a system, the transmitting device comprisingsignal transmission means that transmits over a frequency channel asignal in which ISI is allowed. According to an aspect of the presentinvention, it is possible to improve the usage efficiency of thespectrum to be used for communication and it is also possible to improvethe possibility of the filter for shaping the pulse of the frequencychannel.

The transmitting device according to claim 7 is the transmitting devicein claim 6, wherein the signal transmission means transmits the signalin which the ISI is allowed and in which the bandwidth of the frequencychannel is limited by a pulse shaping filter to Nyquist bandwidth as alower limit. According to an aspect of the present invention, it ispossible to suppress ISI at the waveform level of each frequency channelwithin a range where the receiving side is capable of compensating ISI.

A transmitting device according to claim 8 is a transmitting device thattransmits a signal over frequency channels set by dividing a frequencybandwidth assigned to a system, the transmitting device comprising: aspectrum usage information and policy information acquiring portion thathas a function to detect a bandwidth of a frequency channel that is notbeing currently used and to determine usage status of that frequencychannel; and a pulse shape and symbol rate controller that determineswhether or not a user allows ISI and whether or not an adjacentfrequency channel for another user is interfered, based upon theinformation acquired by the spectrum usage information and policyinformation acquiring portion, and that determines at least one of acenter carrier frequency, a symbol rate, and a pulse shape, based upon adetermination result, wherein the signal generated based upon acondition determined by the pulse condition determination means istransmitted. According to an aspect of the present invention, thetransmitting device is capable of detecting a bandwidth of a frequencychannel that is not being currently used and a usage status of afrequency channel, determining whether or not a user allows ISI andwhether or not an adjacent frequency channel for another user isinfluenced, based upon the information acquired by the spectrum usageinformation and policy information acquiring portion, and determining atleast one of a center carrier frequency, a symbol rate, and a pulseshape, based upon a determination result. It is therefore possible totransmit the signal with a high usage efficiency of the spectrumaccording to the usage status of the spectrum, while the signal qualityof the received signal is being considered, after the pulse shapingfilter decreases the interval between the frequency channels andoccupied bandwidth according to the usage status of the frequency.

A receiving device according to claim 9 is a receiving device thatreceives a signal transmitted over frequency channels set by dividing afrequency bandwidth assigned to a system, the receiving device receivingthe signal transmitted by allowing Inter-Symbol Interference at awaveform level for each of the frequency channels, the transmittingdevice comprising ICI removal means that removes the Inter-ChannelInterference, owing to overlapping adjacent frequency channels with eachother, allowed at the signal transmitted. According to an aspect of thepresent invention, it is possible to remove the interference betweenchannels of the received signal, thereby preventing the degradation ofthe quality of the received signal.

A receiving device according to claim 10 is a receiving device thatreceives a signal over frequency channels set by dividing a frequencybandwidth assigned to a system, the receiving device comprising ISIcompensation means that receives a signal transmitted by allowingInter-Symbol Interference at a waveform level for a frequency channel,and then compensates the Inter-Symbol Interference at the waveform levelfor the frequency channels of the signal transmitted. According to anaspect of the present invention, it is possible to compensate thewaveform of the received signal, thereby preventing the degradation ofthe quality of the received signal.

A method according to claim 11 is a method for communicating overfrequency channels set by dividing a frequency bandwidth assigned to asystem, the method comprising: receiving a signal transmitted byallowing Inter-Channel Interference to overlap the frequency channelsadjacent to each other in a frequency domain; and removing ICI, owing tooverlapping adjacent frequency channels with each other, from the signalreceived. According to an aspect of the present invention, thetransmitting side transmits the signal by overlapping multiple frequencychannels with each other, thereby making the frequency bandwidthassigned to the system available to more frequency channels andimproving the usage efficiency of the spectrum. Also, the receiving sideis capable of removing the interference between frequency channelsgenerated on the overlapping frequency regions, thereby preventing thedegradation in the signal quality of received signal.

A method according to claim 12 is a method for communicating overfrequency channels set by dividing a frequency bandwidth assigned to asystem, the method comprising: receiving a signal transmitted byallowing Inter-Symbol Interference at a waveform level for each of thefrequency channels; and compensating the Inter-Symbol Interference atthe waveform level for each of the frequency channels of the signal outof the signals received in the receiving. According to an aspect of thepresent invention, the transmitting device is capable of transmittingthe signal with a pulse that does not satisfy the zero ISI condition,thereby decreasing the bandwidth of each frequency channel.Consequently, the frequency bandwidth assigned to the system can be usedby more frequency channels, thereby improving the usage efficiency ofthe spectrum. In addition, in shaping the pulse, the zero ISI conditiondoes not have to be considered, thereby improving the design flexibilityof the filter for pulse shaping. Further, since the receiving side iscapable of compensating ISI, the degradation in the signal quality ofthe received signal can be prevented.

A method according to claim 13 is a method for communicating overfrequency channels set by dividing a frequency bandwidth assigned to asystem, the method comprising: acquiring information about a function todetect a bandwidth of a frequency channel that is not being currentlyused and to determine usage status of that frequency channel;determining whether or not a user allows ISI and whether or not anadjacent frequency channel for another user is interfered, based uponthe information acquired in the acquiring; and controlling determinationof at least one of a center carrier frequency, a symbol rate, and apulse shape of a signal transmitted from the transmitting device, basedupon a determination result in the determining. According to an aspectof the present invention, the transmitting device is capable ofdetecting the bandwidth of the frequency channel that is not beingcurrently used, determining whether or not a user allows ISI and whetheror not an adjacent frequency channel for another user is influenced,also determining whether or not it is possible to allow the frequencychannel, for another user, adjacent to the frequency channel tointerfere with the frequency channel, and determining at least one ofthe center carrier frequency, symbol rate, the shaped pulse of thesignal to be transmitted, based on the above determination. Accordingly,it is possible to transmit the signal with a pulse shape of a high usageefficiency of the frequency according to the usage status of thefrequency, while the signal quality of the received signal is beingtaken into consideration.

ADVANTAGEOUS EFFECT OF THE INVENTION

According to an aspect of the present invention, it is possible totransmit the signals where frequency channels bandwidths are narrower,compensate the signal waveform of the frequency channels at thereceiving side or remove the interference between frequency channels. Itis also possible to make the signal transmitted by the transmittingdevice interfere with another frequency channel according to the statusand/or allow the inter-symbol interference at a waveform level forfrequency channels. This enables to provide a communication system,transmitting device, receiving device, and communication method, wherebythe spectrum usage efficiency is high and the signal quality is notdegraded, without the need for users' cooperation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A to FIG. 1C are illustrations of the technical theory of removingICI according to a first embodiment of the present invention;

FIG. 2 is an illustration of a Cyclic Wiener filter;

FIG. 3 is an illustration of an FSE filter;

FIG. 4A to FIG. 4C are illustrations of cyclostationarity according tothe first embodiment of the present invention;

FIG. 5A to FIG. 5C are illustrations of a method of generating a zeroISI signal according to a second embodiment of the present invention;

FIG. 6 is an illustration of a communication system according to thefirst embodiment and according to a fourth embodiment of the presentinvention;

FIG. 7 is an illustration of a state where frequency channels to be usedby multiple users overlap each other according to the first embodimentof the present invention;

FIG. 8 is an illustration of a receiving device according to the firstembodiment of the present invention;

FIG. 9 is an illustration of the allowable range of ICI according to thefirst embodiment of the present invention;

FIG. 10 is a block diagram illustrative of the configuration of thereceiving device according to the second embodiment of the presentinvention;

FIG. 11A to FIG. 11C are illustrations of the allowable range where thebandwidth of the frequency channel is narrowed by allowing ISI accordingto the second embodiment of the present invention;

FIG. 12A to FIG. 12C are illustrations of a procedure of the ISIcompensation according to the second embodiment of the presentinvention;

FIG. 13 is a block diagram illustrative of a configuration of thereceiving device according to the third embodiment of the presentinvention;

FIG. 14 is an illustration of examples of arrangement and shaping offrequency channels according to the third embodiment of the presentinvention;

FIG. 15A to FIG. 15C are flowcharts illustrative of communicationmethods performed according to the first to third embodiments of thepresent invention;

FIG. 16 is an illustration of comparisons of obtainable effects amongthe first to third embodiments of the present invention;

FIG. 17A and FIG. 17B are block diagrams illustrative of a configurationof the transmitting device according to a fourth embodiment of thepresent invention;

FIG. 18A and FIG. 18B are illustrations of another configuration exampleof the transmitting and receiving device illustrated in FIG. 17A andFIG. 17B;

FIG. 19 is a flowchart illustrative of the communication methodaccording to the fourth embodiment of the present invention;

FIG. 20 shows frequency spectrums of a general OFDMA;

FIG. 21 shows frequency spectrums of a general FDMA;

FIG. 22 shows a case where intervals between the frequencies channel aremade narrower by making guard bands smaller; and

FIG. 23 shows another case where the pulse waveform frequency responseis made steep to make the intervals between the frequency channelsnarrower.

EXPLANATION OF REFERENCES

-   -   101 a, 101 b base transceiver station    -   102 a, 102 b transmitting and receiving device    -   103 a, 103 b, 104 a, 104 b, 104 c mobile telephone    -   111 ICI removal and ISI compensation filter    -   151, 161 transmitting unit    -   152 data generator and modulator    -   153 pulse shaping portion    -   154 D/A converter    -   155, 501 RF portion    -   157 spectrum usage information and policy information acquiring        portion    -   158 pulse shape and symbol rate controller    -   159 center carrier frequency controller    -   401 transmitting and receiving portion    -   502 A/D converter    -   503, 504, 505 channel selection filter    -   506 ICI removal filter    -   801 ISI compensation filter

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, first to fourth embodiments will be described withreference to accompanied drawings. In the description of each of theembodiments, the drawing or description for the same configuration willbe partially omitted. In addition, the same components andconfigurations as those employed before have the same referencenumerals.

1 Technical Theory

Firstly, before embodiments of the present invention are described, adescription will be given of the technical theory of signal processingfor removing the interference, to be performed according to the first tofourth embodiments.

The first embodiment is applicable to the multiple access, in which datatransmitted from communication terminal devices of the respective usersat multiple points are multiplexed in an efficient. Hereinafter, theprinciple of the multiple access according to the present invention willbe described first before the principles of a communication system,transmitting device, receiving device, and communication method aredescribed.

(1) Removal of ICI

A method for removing ICI (Inter-Channel Interference) will firstly bedescribed. The ICI is removed according to the first embodiment, becauseICI that is the interference between channels occurs in a case wherezero ISI is satisfied at the transmitting side and the frequencies areoverlapped with each other to decrease the intervals between thefrequency channels.

FIG. 1A, FIG. 1B, and FIG. 1C are illustrations of the technical theoryof removing ICI according to the first embodiment of the presentinvention. The removal of ICI is achieved with the use of filterscapable of exploiting cyclostationarity such as a Cyclic Wiener Filteror an FSE (Fractionally Spaced Equalizer) filter.

An adaptive filter for ICI removal utilizes the cyclostationarity ofsignals, so that the frequency component outside the Nyquist bandwidth(excessive bandwidth frequency component), which is interfered byoverlapping adjacent frequency channels can be restored by use of thefrequency components inside the Nyquist bandwidth (informationbandwidth) that is not influenced by the interference.

FIG. 2 is an illustration of the outline of a Cyclic Wiener filter. FIG.3 is an illustration of an FSE filter. Referring to FIG. 2, the CyclicWiener filter includes multiple FSE filters 201 connected in parallelwith each other to combine the outputs from the FSE filters 201. Thecombined outputs are subtracted from a desired signal and an errorsignal is calculated. Each of the filter coefficients of the FSE filters201 is adjusted to make the error signal small.

Referring now to FIG. 3, the FSE filter 201 includes a series of delayelements 301 that delay the oversampled signal to be input, so acoefficient or a weight ci is multiplied with the respective outputs andare combined. Such a group of coefficients are referred to as tapcoefficient. Incidentally, since the Cyclic Wiener filter and the FSEfilter 201 are known as described in Document 1 and Document 2 to belisted below, the detailed description thereof will be omitted.

Document 1: W. A. Gardner, “Exploitation of spectral redundancy” incyclostationary signals”, IEEE Signal Processing Magazine, vol. 8, no.2, pp. 14-36, April 1991

Document 2: W. A. Gardner, “Cyclic Wiener filtering: theory and method”,IEEE Trans. Commun, vol. 41, no. 1, pp. 151-163, January 1993

In the example illustrated in FIG. 1A, the frequency channel indicatedby P in the middle of the three frequency channels is to be processed.In this situation, there are overlapping regions between the frequencychannel P and its adjacent frequency channels, respectively. Hence, thefrequency channel P is incurred by the influence of the interferencefrom the adjacent frequency channels. According to the cyclostationarityof signals, as illustrated in FIG. 1C, there is a high correlationbetween the frequency component of a range D and the frequency componentof a range B, and there is a high correlation between the frequencycomponent of a range C and the frequency component of a range A. Thisenables the signal component of the range D to be restored by use of thesignal component of the range B, and also enables the signal componentof the range C to be restored by use of the signal component of therange A, according to the present embodiment. A frequency range E ofFIG. 10 represents the Nyquist bandwidth.

Hereinafter, the cyclostationarity will be briefly described. FIG. 4Aillustrates a state where digitally converted signals are periodicallytransmitted at a symbol interval Ts. FIG. 4B illustrates spectrums ofthe signals illustrated in FIG. 4A. By shaping the spectrums of FIG. 4Binto pulses, the pulse signals of FIG. 4C are obtained. According to thecyclostationarity of the spectrums illustrated in FIG. 4B, in the pulsesignals of FIG. 4C, there is a correlation between the frequencycomponents in the Nyquist bandwidth (B′, D′) and the excessive bandwidthfrequency component (B, D). The excessive bandwidth refers to thebandwidth which the remaining signal bandwidth after excluding theNyquist bandwidth from the occupied bandwidth.

In the first embodiment, ICI is allowed by overlapping the frequencychannels by use of the correlation of the frequency components at eachfrequency channel, to remove the interference between channels (ICI) atthe receiving side. The interference removal between the frequencychannels is performed for each frequency channel by an ICI removalfilter.

(2) Zero ISI

FIG. 5A and FIG. 5B are illustrations of a method for removing ISI(Inter-Symbol Interference) to generate signals of zero ISI according toa second embodiment. FIG. 5A is an illustration of an example of thefrequency response of a raised cosine pulse that satisfies theconditions for zero ISI.

In FIG. 5A, the horizontal axis represents frequency f, and the verticalaxis represents pulse Frequency Response. Vestigial symmetry issatisfied for the boundary line (+0.5/Ts, −0.5/Ts) of the Nyquistbandwidth [−0.5/Ts, 0.5/Ts] (where the symbol rate is 1/Ts). Thecondition for satisfying the Vestigial symmetry is that all regions A,B, C, and D in FIG. 5A are equal to each other (A=B=C=D). In the secondembodiment, the condition for satisfyingA=B=C=Disazero ISI condition.

Additionally, the Nyquist frequency is a half the symbol rate (where thesymbol rate is 1/Ts, the Nyquist frequency is 0.5/Ts). The Nyquistbandwidth ranges from −0.5/Ts to 0.5/Ts, with 0 Hz being in the middle.

FIG. 5B illustrates an example in which a pulse satisfying the conditionA=B=C=D of FIG. 5A is sampled. The pulse's frequency response is foldedafter sampling due to aliasing, and such folded signals are added tofinally obtain the flat spectrum of FIG. 5C. That is to say, the pulse'sfrequency response that enables zero ISI at the waveform level turns tobe flat after sampling.

In the second embodiment, the above characteristic is employed. In otherwords, induction of artificial ISI (Inter-Symbol Interference) isallowed at a waveform level at the transmitting side before multiplexingof multiple transmission signals. On the other hand, the ISI iscompensated at the waveform level of a signal at the receiving side toremove Inter-Symbol Interference (ISI).

First Embodiment

(Communication System)

The outline of a communication system according to a first embodimentwill now be described. FIG. 6 is a view illustrative of a communicationsystem according to the first embodiment and according to a fourthembodiment. The communication system according to the first embodimentis a communication system that utilizes the frequency channels set bydividing the frequency into multiple bandwidths.

As illustrated, the communication system according to the presentembodiment includes base transceiver stations 101 a and 101 b, andmobile telephones 103 a, 103 b, 104 a, 104 b, and 104 c that communicatewith another communication terminal device via the base transceiverstations 101 a and 101 b. Both the communication areas which can bemanaged by the base transceiver stations 101 a and 101 b are referred toas communication management area a.

The mobile telephones 103 a and 103 b are served by the sametelecommunications carrier, whereas the mobile telephones 104 a, 104 b,and 104 c are served by a telecommunications carrier different from thatwhich serves the mobile telephones 103 a and 103 b. In addition, in FIG.6, all the communication terminal devices that communicate in thecommunication system are represented as mobile telephones. However, thefirst embodiment is not limited to such a configuration. This isapplicable to any communication terminal device that can communicatewith the communication system.

The base transceiver stations 101 a and 101 b are provided withtransmitting and receiving devices 102 a and 102 b, respectively. Thetransmitting and receiving device 102 a receives signals that the mobiletelephones 103 a, 104 a, and 104 b respectively transmit over thefrequency channels, and then multiplexes the received signals. Suchmultiplexed signals are transmitted to the base transceiver station 101b via a device for an upper layer.

The transmitted signals are received by the transmitting and receivingdevice 102 b, and are then transmitted to the mobile telephone 103 b or104 to be received.

The mobile telephones 103 a and 103 b as well as the mobile telephones104 a, 104 b, and 104 c are also provided with transmitting andreceiving portions 401, respectively.

In the first embodiment, all of multiple transmitting and receivingportions 401 of multiple mobile telephones each serve as a transmittingdevice, whereas the transmitting and receiving devices 102 a and 102 beach serve as a receiving device. However, the present invention is notlimited to the above configuration. The transmitting and receivingdevices may have any configuration as far as the transmitting devices inmultiple access transmit radio signals and the receiving devices receivethe radio signals that have been transmitted.

(Transmitting Device)

The transmitting device according to the first embodiment of the presentinvention will be described. As described above, the users of the mobiletelephones 103 a, the 104 a, and the 104 b are different from eachother. For this reason, the mobile telephone 103 a communicates with thebase transceiver station 101 a, over a single or multiple frequencychannels different from that or those of the mobile telephones 104 a and104 b.

As an example, a description will be given of a case where the frequencychannel of the mobile telephone 103 a and the frequency channels of themobile telephones 104 a and 104 b are adjacent on the frequency.Additionally, in the first embodiment, each of the frequency channels issupposed to satisfy the zero ISI so as not to generate ISI.

FIG. 7 illustrates the frequency channels to be used for transmission ofthe signals of the mobile telephones 103 a, 104 a, and 104 b accordingto the first embodiment. The frequency channels illustrated in FIG. 7overlap each other while the pulse shaping of each frequency channelsatisfies the condition for the zero ISI. Incidentally, as to the pulseshaping filter of the frequency channels, the pulses are shaped at eachof the transmitting and receiving portion 401 at the transmitting sideso that the pulses satisfy the zero ISI condition.

That is to say, the transmitting device according to the firstembodiment is provided for transmitting the signals with the adjacentmultiple frequency channels overlapping each other in the frequencydomain.

In addition, in the frequency channels of the transmission signals, theintervals between the frequency channels are made narrower byoverlapping. To accommodate the ICI within an allowable range at thereceiving side, the overlapping range might be limited to a part of theexcessive bandwidth.

Further, the transmitting device according to the first embodiment isnot limited to a group of multiple communication terminal devices, butmay employ a single configuration for transmitting the signals while themultiple frequency channels are being overlapped.

(Receiving Device)

FIG. 8 illustrates the receiving device according to the firstembodiment. The receiving device is provided with ICI removal filters506 that remove the interference between frequency channels generated inthe overlapped region, out of the transmitted signals. In such aconfiguration, the ICI removal filter 506 corresponds to ICI removalmeans.

The receiving device is also provided with multiple channel selectionfilters 503, 504, and 505. Such filters are provided for selecting thefrequency channel for the transmitted signal, when a user uses multiplefrequency channels.

That is to say, the receiving device illustrated in FIG. 8 receives, forexample, signals transmitted by a user k. The received signal isdown-converted by an RF portion 501, and is then converted into digitalsignals by an A/D converter 502. If the user k utilizes M frequencychannels, the receiving device extracts multiple frequency channels thatthe user k used for communication with the use of M channel selectionfilters. In the example illustrated in FIG. 8, the signal that the userk transmitted passes through the channel selection filter 504.

In addition, in the first embodiment, the pulse waveforms of thefrequency channels after reception of the signals satisfy the zero ISIcondition. The pulse shaping for satisfying the zero ISI condition maybe performed at the transmitting device beforehand as described in thefirst embodiment, or a filter for shaping the pulse waveforms incooperation with the pulse waveform shaping filter, not illustrated, ofthe transmitting device may be provided at the receiving device.

Furthermore, the frequency bandwidth in which the respective frequencychannels are overlapped is limited within the excessive bandwidth range,thereby allowing the ICI removal filter 506 to remove ICI within theexcessive bandwidth range. FIG. 9 illustrates an allowable range of ICI.In a case where a symbol rate is 1/Ts and a roll-off coefficient forpulse shaping is α, the ICI allowable range is represented by α/2Ts, asillustrated in FIG. 9.

Incidentally, the ICI allowable range is influenced by the strength ofthe signal transmitted over the frequency channel. If a frequencychannel of a signal has a power too weak to influence the frequencychannel, it may interfere with the Nyquist bandwidth of the adjacentfrequency channel.

Also, a cyclic Wiener filter that utilizes the cyclostationarity or anFSE filter may be used for the ICI removal filter 506.

According to the first embodiment described heretofore, the transmittingside is capable of transmitting the overlapped signal while satisfyingthe ISI zero condition, whereas the receiving side is capable ofremoving interference between frequency channels by removing the ICIgenerated by overlapping. It is therefore possible to provide acommunication system, transmitting device, receiving device, andcommunication method, whereby the usage efficiency of the frequencies ishigh and the signal quality is not degraded, without the need forcooperation among multiplexed users.

Second Embodiment

A second embodiment of the present invention will now be described. Inthe second embodiment, a description will be given of the receivingdevice that receives the signal of the frequency channel that does notsatisfy the zero ISI condition, and that performs the ISI compensationat the receiving device side. In the second embodiment, the transmittingside does not make the pulse signals overlapped.

In the second embodiment, the transmitting and receiving portions 401 ofthe mobile telephones 103 a, 104 a, and 104 b serve as signaltransmitting means that allows the ISI in multiple frequency channelsand then transmits the signals.

FIG. 10 is a block diagram illustrative of the configuration of thereceiving device according to the second embodiment. The receivingdevice illustrated in FIG. 10 is provided with the RF portion 501 andthe A/D converter 502 as with the receiving device illustrated in FIG.8. However, the receiving device illustrated in FIG. 10 is differentfrom that of FIG. 8 in that ISI compensation filters 801 are providedinstead of the ICI removal filters 506. The ISI compensation filter 801serves as ISI compensation means according to the present embodiment.

The ISI compensation filter is achieved with an adaptive filter thatutilizes the cyclostationarity. As an adaptive filter, for example, theCyclic Wiener filter, FSE filter or the like may be employed.

FIG. 11A is an illustration of signals received by the receiving deviceaccording to the second embodiment. In the illustrated frequencychannels, the pulse shaping of each channel does not satisfy the zeroISI condition. Such signals have poor signal quality subsequent to thereception, due to the influence of ISI, so may not transmit theinformation with accuracy. In the second embodiment, even in a casewhere such signals are received, the communication with high signalquality and high usage efficiency of frequencies are achieved bycompensating the ISI at the receiving side.

FIG. 11B and FIG. 11C are illustrations of an allowable range in whichthe bandwidth of the frequency channels is narrowed by the allowingnon-zero ISI. FIG. 11B illustrates the shapes of the frequency channelsin a case where the zero ISI condition is satisfied without employingthe method in the second embodiment. In this case, the bandwidth of thefrequency channels is represented by (1+α)/Ts, where a symbol rate is1/Ts and a roll-off coefficient for satisfying the zero ISI condition isα. FIG. 11C illustrates a case where the bandwidth of the frequencychannels is made narrower by use of the method according to the secondembodiment. In this case, the bandwidth of the frequency channels ismade narrower to the Nyquist bandwidth (=1/Ts). This permits thebandwidth of the frequency channels to be narrower by α/Ts.

FIG. 12 is an illustration of a procedure of the ISI compensationaccording to the second embodiment. The ISI compensation according tothe second embodiment is supposed to process the frequency channelindicated by P in the middle out of three frequency channels illustratedin FIG. 12A. The frequency channel P to be processed is extracted by thechannel selection filter (FIG. 12B), and then the ISI component of theextracted frequency channel P is compensated by the ISI compensationfilter 801. Consequently, the signals adjusted to satisfy the zero ISIcondition are output from the ISI compensation filter 801 (FIG. 12C).

Additionally, as a preferable pulse for shaping that does not satisfythe zero ISI condition in the second embodiment, there is a pulse thatsatisfies the following two expressions.

X(f)=cos(πfTs/(1+α)) for |f|(1+α)/2Ts

and

X(f)=0 for otherwise

Such a pulse has relatively small excess bandwidth (α/Ts) and the shapeof its frequency response is smooth.

According to the second embodiment as described above, it is madepossible for the transmitting device to transmit the signals with thepulse that does not satisfy the zero ISI condition, thereby making smallthe bandwidth of each of the frequency channels. This allows thefrequency bandwidth assigned to the system to be used by more frequencychannels, thereby increasing the usage efficiency of the spectrum.Moreover, in shaping the pulse, the zero ISI condition does not have tobe considered, thereby increasing the design flexibility of the filterused for pulse shaping.

Third Embodiment

A third embodiment of the present invention will now be described. Inthe third embodiment, a description will be given of a receiving device,which includes the characteristics of the first embodiment and thesecond embodiment, and which is provided with both the ICI removalfilter and the ISI compensation filter at the receiving device side.

FIG. 13 is a block diagram illustrative of a configuration of thereceiving device according to the third embodiment. The receiving deviceillustrated in FIG. 13 is provided with the RF portion 501 and the A/Dconverter 502 as with the receiving device illustrated in FIG. 8 andFIG. 10, and is further provided with an ICI removal and ISIcompensation filter 111. The ICI removal and ISI compensation filter 111is a filter in which the functions of the ICI removal filter 506 and theISI compensation filter 801, described above, are combined and which isachievable by an adaptive filter. As an adaptive filter, for example, aCyclic Wiener filter or FSE filter may be used.

FIG. 14 is an illustration of frequency channels preferable to shape thepulse waveforms at the receiving device according to the thirdembodiment. In FIG. 14, the horizontal axis represents frequency and thevertical axis represents frequency response of the pulse. The frequencychannels having such waveforms overlap each other without satisfying thezero ISI condition.

The signal received by the receiving device illustrated in FIG. 13 isdown-converted by the RF portion 501, is then converted into digital bythe A/D converter 502, and further passes through any one ofcorresponding channel selection filters. Subsequently, the ICI removaland ISI compensation filter 111 removes ICI and compensates for ISI.

According to the third embodiment as described, the transmitting sidetransmits the signals overlapping each other with the pulses that do notsatisfy the zero ISI condition, and the receiving side performs ISIcompensation. Simultaneously, it is possible to remove ICI generated byoverlapping frequency channels and compensate for ISI owing to the useof non-zero ISI shaping filters to shape frequency channels. This allowsthe bandwidth of each frequency channel to be narrower. Also, thefrequency channels are overlapped for transmission, thereby allowing thefrequency bandwidth assigned to the system to be used by more frequencychannels. It is therefore possible to improve the usage efficiency ofthe spectrum. Moreover, in shaping the pulse, the zero ISI conditiondoes not have to be considered, thereby increasing the designflexibility of the filter that performs the pulse shaping.

It is therefore possible to provide a communication system, transmittingdevice, receiving device, and communication method, whereby the usageefficiency of the frequency is high and the signal quality is notdegraded, even if the multiplexed users do not cooperate with eachother.

(Communication Method)

FIG. 15A, FIG. 15B, and FIG. 15C are flowcharts illustrative ofcommunication methods performed in the first to third embodiments asdescribed heretofore. The flowcharts illustrated in FIG. 15A, FIG. 15B,and FIG. 15C include the same processes. In the drawings, the sameprocesses are indicated by the same numerals.

Referring to FIG. 15A, in the first embodiment, the receiving devicereceives a signal from the transmitting device (S131). Then, thereceiving device uses multiple channel selection filters to extract thefrequency channel of the signal to be received (S132). Then, thereceiving device uses an ICI removal filter suitable for the frequencychannel extracted by the channel selection filter, and removes ICI fromthe received signal (S133).

In addition, in the second embodiment, the receiving device receives asignal from the transmitting device (S131). Then, the receiving deviceuses multiple channel selection filters to extract the frequency channelof the signal to be received (S132). The receiving device uses an ISIcompensation filter suitable for the frequency channel extracted by thechannel selection filter, and compensates ISI of the received signal(S134).

Furthermore, in the third embodiment, the receiving device receives asignal from the transmitting device (S131). Then, the receiving deviceuses multiple channel selection filters to extract the frequency channelof the signal to be received (S132). The receiving device uses an ICIremoval and ISI compensation filter suitable for the frequency channelextracted by the channel selection filter, and removes ICI of thereceived signal and compensates ISI thereof (S135).

(Comparisons of the First to Third Embodiments)

FIG. 16 is an illustration of comparisons of obtainable effects in thefirst to third embodiments. In the drawing, the communication of FDMAshown in FIG. 21 is represented by conventional method 1 and thecommunication of OFDMA shown in FIG. 20 is represented by conventionalmethod 2. Also, the communication method according to the firstembodiment is represented by proposed method 1, the communication methodaccording to the second embodiment is represented by proposed method 2,and the communication method according to the third embodiment isrepresented by proposed method 3.

Also in FIG. 16, with respect to the above five methods, four itemsincluding spectrum usage efficiency, magnitude of temporal dispersion inthe time response of the pulse, presence or absence of Inter-ChannelInterference (ICI), presence or absence of Inter-Symbol Interference(ISI) are compared. As illustrated, the communication method or thecommunication system and the receiving device according to the first tothird embodiments are capable of improving the efficiency of thespectrum usage, as compared to the conventional technique, and arecapable of decreasing the magnitude of temporal dispersion in the timeresponse of the shaping filter used to shape each frequency channel.Additionally, ICI, ISI, or both of them are permitted and transmitted,so that the receiving side can remove and compensate them to extract thesignals of each frequency channel in good quality.

Fourth Embodiment

A fourth embodiment will now be described. A communication systemaccording to the fourth embodiment is a communication system thatcommunicates over frequency channels, and is provided with atransmitting device that transmits signals and a receiving device thatreceives the signals transmitted by the transmitting device. Accordingto the fourth embodiment, the transmitting and receiving device 102 billustrated in FIG. 6 is supposed to be a transmitting device and themobile telephones 103 b and 104 c in the management area a are supposedto be receiving devices.

FIG. 17A and FIG. 17B are block diagrams illustrative of a configurationof the transmitting device according to the fourth embodiment. FIG. 17Ais a view illustrative of a configuration of the transmitting device andFIG. 17B is a view illustrative of multiple users using multiplefrequency channels.

Referring to FIG. 17B, in multiple access, multiple users (user 1, . . ., and user N) use multiple channels (for example, the user k usesfrequency channels f_(k1), f_(k2), . . . , and f_(kM)) to transmitmultiple data streams in parallel. In FIG. 17B, the horizontal axisrepresents frequency.

In the drawing, identical hatching patterns denote the frequencychannels used by the same user. In this situation, the user 1 usesfrequencies f₁₁ and f_(1k′), and the user k uses the frequencies f_(k1)and f_(kM). As is obvious from the drawing, each user uses one or morefrequency channels.

The transmitting device illustrated in FIG. 17A includes a transmittingunit 151 that generates a transmission signal for each user, shapes thepulse waveform, and transmits the signal. The transmitting unit 151 isprovided with: a data generator and modulator 152 that generates data ofinformation to be transmitted on each frequency channel and generatesthe transmission signal by modulating the signal by use of the data; apulse shaping portion 153 that shapes the pulse waveform of thetransmission signal; a D/A converter 154 that converts the shaped pulsewaveform from a digital signal to an analog signal; an RF portion 155that up-converts the analog baseband signal; and an antenna 156 thattransmits the signal.

The transmitting unit 151 is provided with: a spectrum usage informationand policy information acquiring portion 157; a pulse shape and symbolrate controller 158; and a center carrier frequency controller 159. Thespectrum usage information and policy information acquiring portion 157has a function of detecting the bandwidth of the frequency channel thatis not currently being used and a function of acquiring usage status ofother users frequency channels or a function of acquiring policyinformation on whether or not another user is provided with a functionof removing ICI.

The spectrum usage information and policy information acquiring portion157 is capable of acquiring the usage status or the policy informationof the frequency channel with the following configuration. For instance,users are supposed to share the spectrum usage policy (such as a userclass ID, and information on possibility or impossibility of overlappingwith each user class) as defined by the policy information beforehand.

Each user is able to determine the signal strength, specifications, orpresence or absence of an ICI removal function for adjacent frequencychannels, by determining the user class from the spectrum of theadjacent frequency channel over the frequency. If the presence of theICI removal function is determined, it is possible to allow theoverlapping the frequency channel with the adjacent frequency channel.

In addition, in the fourth embodiment, it is possible to set a controlchannel beforehand so that users can exchange information. Such aconfiguration allows a user of an adjacent frequency channel todetermine spectrum usage information and policy information; i.e.,whether or not overlapping is allowed via the control channel.

Furthermore, a database may be provided for storing and updating theusage status of the spectrum or frequency usage policy sequentially. Inthe database, which user class uses which channel is registered, so thateach user accesses the data to determine whether or not overlapping withan adjacent channel is possible.

The pulse shape and symbol rate controller 158 uses the bandwidthinformation of the frequency channel that is not currently being usedand the spectrum usage information, which are acquired by the spectrumusage information and policy information acquiring portion 157 todetermine the number of the frequency channels to be used for signaltransmission, the center carrier frequency in each frequency channel,the symbol rate, and the pulse shape so as to determine the bandwidth ofthe frequency channel that is not currently being used.

The center carrier frequency controller 159 communicates with the RFportion 155 the center carrier frequency information of each frequencychannel, which has been determined by the pulse shape and symbol ratecontroller 158, in multiple frequency channels to be used for signaltransmission. The RF portion 155 up-converts the signal based upon thecenter carrier frequency information of each frequency channel that hasbeen communicated from the center carrier frequency controller 159, andtransmits the signal via the antenna 156.

With the above configuration, the pulse shape and symbol rate controller158 serves as frequency channel determination means, overlap possibilityor impossibility determination means, and pulse shaping typedetermination means.

FIG. 18A is an illustration of another configuration example of thetransmitting and receiving device illustrated in FIG. 17A. Atransmitting unit 161 illustrated in FIG. 18A is provided with one D/Aconverter 154 and one RF portion 155 for a single user, and is differentfrom the configuration of FIG. 17A in that they are shared by multiplefrequency channels. According to the configuration illustrated in FIG.18A, the number of parts is made smaller than that of the transmittingdevice illustrated in FIG. 17A, thereby producing advantages ofdownsizing of the device and cost reduction thereof.

FIG. 19 is a flowchart illustrative of the communication methodaccording to the fourth embodiment. The transmitting device according tothe fourth embodiment receives a request that a user who is notcurrently in communication (new user) utilizes the communication systemfor communication (S171). The spectrum usage information and policyinformation acquiring portion 157 determines availability status of thefrequency channel, and also acquires the spectrum usage information(spectrum usage policy) (S172).

Also, the pulse shape and symbol rate controller 158 determines basedupon the spectrum usage policy acquired by the spectrum usageinformation and policy information acquiring portion 157, whether or notit is possible to add overlapping with a frequency channel adjacent tothe frequency channel determined to be available at step S172.

At step S173, when the overlapping is determined to be impossible (S173:No), the pulse shape and symbol rate controller 158 further determineswhether or not the receiving device is provided with the ISIcompensation functionality and it is therefore possible to compensateISI when the ISI is introduced into the signal transmitted from thetransmitting unit (S174). As a result of the determination, when thereceiving side is not capable of compensating ISI (S174: No), thetransmission signal is determined to have a pulse waveform (conventionalpulse shape) into which ISI is not introduced same as in conventionalcase (S176).

Also, at step S174, when the receiving side is determined to be capableof compensating ISI (S174: Yes), the pulse shape and symbol ratecontroller 158 determines that the transmission signal should have thepulse waveform (proposed pulse shape (2)) described in the secondembodiment of the present invention (S177).

Meanwhile, at step S173, when overlapping with an adjacent frequencychannel is determined to be possible (S173: Yes), the pulse shape andsymbol rate controller 158 determines whether or not the receivingdevice is provided with the ISI compensation functionality and it istherefore possible to compensate ISI when the ISI is introduced into thesignal transmitted from the transmitting unit (S175).

As a result of the determination at step S175, when the receiving sideis not capable of compensating ISI (S175: No), the transmission signalis determined to have a pulse waveform (proposed pulse shape (1)) thathas been described in the first embodiment of the present invention(S178). Also, at step S175, when the receiving side is determined to becapable of compensating ISI (S175: Yes), the pulse shape and symbol ratecontroller 158 determines to make the transmission signal have the pulsewaveform (proposed pulse shape (3)) that has been described in the thirdembodiment of the present invention (S179).

The pulse shape and symbol rate controller 158 determines the centercarrier frequency and symbol rate of the transmission signal based uponthe determined pulse waveform (S180).

The center carrier frequency controller 159 communicates such determinedcenter carrier frequency with the RF portion 155. Then, necessaryparameters out of the parameters determined by the receiving device arecommunicated and a communication is initiated (S181).

According to the fourth embodiment described above, it is made possibleto make another frequency channel interfere with the signal transmittedby the transmitting device in accordance with the status, or make thetransmission signals overlap with each other. Moreover, when thereceiving side is capable of compensating ISI, the bandwidth of thefrequency channel is made narrow by allowing ISI. It is thereforepossible to provide a communication system, receiving device, andcommunication method, whereby usage efficiency of the spectrum is highand signal quality is not degraded, even if multiplexed users do notcooperate with each other.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a communication system,transmitting device, receiving device, and communication method, to beapplied to the environment where a single or multiple frequency channelsare used without cooperation among multiplexed users.

1. A communication system that communicates over frequency channels setby dividing a frequency bandwidth assigned to the system, thecommunication system comprising: a transmitting device that transmits asignal in which Inter-Channel Interference is allowed by purposelyoverlapping among the frequency channels adjacent to each other in afrequency domain; and a receiving device that receives the signaltransmitted from the transmitting device, the receiving devicecomprising ICI removal means that removes the Inter-ChannelInterference, owing to overlapping adjacent frequency channels with eachother, allowed at the signal transmitted.
 2. A communication system thatcommunicates over frequency channels set by dividing a frequencybandwidth assigned to the system, the communication system comprising: atransmitting device that transmits a signal in which Inter-SymbolInterference at a waveform level for each of the frequency channels isallowed; and a receiving device that receives the signal transmittedfrom the transmitting device, the receiving device comprising ISIcompensation means that compensates Inter-Symbol Interference at thewaveform level incurred at the signal transmitted for each of thefrequency channels.
 3. A communication system that communicates overfrequency channels set by dividing a frequency bandwidth assigned to thesystem, the communication system comprising: a transmitting device thattransmits a signal; a receiving device that receives the signaltransmitted from the transmitting device; a spectrum usage informationand policy information acquiring portion that has a function to detect abandwidth of a frequency channel that is not being currently used and todetermine usage status of that frequency channel; a pulse shape andsymbol rate controller that determines whether or not a user allows ISIand whether or not an adjacent frequency channel for another user isinterfered, based upon the information acquired by the spectrum usageinformation and policy information acquiring portion, and thatdetermines at least one of a center carrier frequency, a symbol rate,and a pulse shape, based upon a determination result; and a centercarrier frequency controller that controls a center carrier frequency ofthe signal transmitted with the use of a center carrier frequencydetermined by the pulse shape and symbol rate controller.
 4. Atransmitting device that communicates over frequency channels set bydividing a frequency bandwidth assigned to a system, the transmittingdevice comprising signal transmission means that transmits a signal inwhich adjacent frequency channels are overlapped with each other in afrequency domain.
 5. The transmitting device according to claim 4,wherein the signal transmission means sets overlapping between thefrequency channels of the signal within an excessive bandwidth of afrequency channel.
 6. A transmitting device that communicates overfrequency channels set by dividing a frequency bandwidth assigned to asystem, the transmitting device comprising signal transmission meansthat transmits over a frequency channel a signal in which ISI isallowed.
 7. The transmitting device according to claim 6, wherein thesignal transmission means transmits the signal in which the ISI isallowed and in which the bandwidth of the frequency channel is limitedby a pulse shaping filter to Nyquist bandwidth as a lower limit.
 8. Atransmitting device that transmits a signal over frequency channels setby dividing a frequency bandwidth assigned to a system, the transmittingdevice comprising: a spectrum usage information and policy informationacquiring portion that has a function to detect a bandwidth of afrequency channel that is not being currently used and to determineusage status of that frequency channel; and a pulse shape and symbolrate controller that determines whether or not a user allows ISI andwhether or not an adjacent frequency channel for another user isinterfered, based upon the information acquired by the spectrum usageinformation and policy information acquiring portion, and thatdetermines at least one of a center carrier frequency, a symbol rate,and a pulse shape, based upon a determination result, wherein the signalgenerated based upon a condition determined by the pulse conditiondetermination means is transmitted.
 9. A receiving device that receivesa signal transmitted over frequency channels set by dividing a frequencybandwidth assigned to a system, the receiving device receiving thesignal transmitted by allowing Inter-Symbol Interference at a waveformlevel for each of the frequency channels, the transmitting devicecomprising ICI removal means that removes the Inter-ChannelInterference, owing to overlapping adjacent frequency channels with eachother, allowed at the signal transmitted.
 10. A receiving device thatreceives a signal over frequency channels set by dividing a frequencybandwidth assigned to a system, the receiving device comprising ISIcompensation means that receives a signal transmitted by allowingInter-Symbol Interference at a waveform level for a frequency channel,and then compensates the Inter-Symbol Interference at the waveform levelfor the frequency channels of the signal transmitted.
 11. A method forcommunicating over frequency channels set by dividing a frequencybandwidth assigned to a system, the method comprising: receiving asignal transmitted by allowing Inter-Channel Interference to overlap thefrequency channels adjacent to each other in a frequency domain; andremoving ICI, owing to overlapping adjacent frequency channels with eachother, from the signal received.
 12. A method for communicating overfrequency channels set by dividing a frequency bandwidth assigned to asystem, the method comprising: receiving a signal transmitted byallowing Inter-Symbol Interference at a waveform level for each of thefrequency channels; and compensating the Inter-Symbol Interference atthe waveform level for each of the frequency channels of the signalreceived.
 13. A method for communicating over frequency channels set bydividing a frequency bandwidth assigned to a system, the methodcomprising: acquiring information about a function to detect a bandwidthof a frequency channel that is not being currently used and to determineusage status of that frequency channel; determining whether or not auser allows ISI and whether or not an adjacent frequency channel foranother user is interfered, based upon the information acquired in theacquiring; and controlling determination of at least one of a centercarrier frequency, a symbol rate, and a pulse shape of a signaltransmitted from the transmitting device, based upon a determinationresult in the determining.